married needles (helicopter operation). The needles (pointers) of a dual tachometer indicator installed in a helicopter are said to “married” when one needle is exactly on top of the other.
One needle is driven by a tachometer generator on the engine and the other by a generator on the transmission that senses the speed of the rotor. When the rotor-drive clutch is fully engaged and there is no slippage, the needles are married.
Martin clip (fabric covering component). A patented wire clip used to attach aircraft fabric to the wing ribs. A Martin clip is long piece of spring steel wire with a series of hooks bent into it at each location the fabric should be attached to the rib cap strip. The hooks are pressed through small slits in the reinforcing tape and the fabric and through elongated holes in the rib cap strips. The hooks lock the clip in the holes and pull the fabric tight against the cap strip.
The use of Martin clips rather than rib stitching saves a tremendous amount of time when covering an aircraft surface.

masking tape. Paper tape with a pressure-sensitive adhesive on one side. Masking tape has a wrinkled texture so it will lie smoothly around a curve, and the adhesive is easily removed from a properly prepared surface. Masking tape is used to fasten paper to parts of a surface being painted, to prevent the paint from reaching certain areas.
Masonite. The registered trade name for a type of fiberboard. Masonite is made by exploding wood chips in a steam gun to break them into long, individual fibers. These fibers are bonded together with lignin (a natural adhesive in the original wood) to make a smooth, grainless sheet of material that can be used for insulation, partitions, etc.